• First interation
    • General Scheme
      • Skimmed periodic trigger events are used as background overlay on top of simulated data.
      • These are stored in digi format, in bins of McIlwain-L. Input files are selected by bin, events then selected "randomly".
      • Overlay is done by merging digis for CAL and TKR with a placeholder for ACD as well.
    • Status - tagged and is ready to be incorporated into a GR tag on a branch.
    • Plan - run as part of the system tests.
      • Exercise the code to look for any general issues.
      • Directly compare before and after.
    • The problem - how to get the correct calibration constants for the input background digis. 
      • Only *one* event time can be active at a time in Gaudi.
      • Periodic triggers can be taken at different times corresponding to different calibrations, and the simulation can be done with calibrations corresponding to yet other times.
      • The scheme only works correctly for MC generation where "ideal" calibration constants are used, which is clearly not useful for generating "real data."
  • Upgrade in progress
    • Get the correct calibration constants to the background digi data
      • Rewrite the background files with their calibrations applied, leaving them in a form that doesn't need "calibration".
      • Save information in a new set of overlay data classes.
    • For CAL and ACD, merge the info a the MC stage, before digis are created.
      • In the CAL, trigger info needs to be generated before digitization
    • The production of background overlay files will now be a two step process:
      • Skim jobs to pull out periodic triggers from the data
      • Conversions jobs which run at least part of the reconstruction on these files, convert to these new TDS classes and output them to new background overlay files.
  • Tasks
    • New TDS classes ???
    • Modify the overlay code to access the new classes. ??
    • New code to merge the results of ACD and CAL simulation with the overlay info ?
    • Create PDS (Root) equivalents (new package overlayRootData)
    • Convert periodic-trigger Digi files to the new format
    • Incorporate into system tests
  • ETA: November 26.
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